Polymeric hydrocyanic acids, so-called azulmic acids, and several processes for their preparation have already been described (compare Houben-Weyl, volume 8 (1952), page 261; German Patent Specification No. 662,338 and German Patent Specification No. 949,060. Thus, polymeric hydrocyanic acid is obtained, for example, by heating monomeric hydrocyanic acid to the reaction temperature in dilute aqueous solution in the presence of basic catalysts, such as ammonia, sodium cyanide, sodium cyanate, potassium cyanate or alkaline earths, and, after the reaction has started, taking care that a reaction temperature of 120.degree. C. is not exceeded by cooling the mixture (compare German Patent Specification No. 662,338). In a particular variant of this process, further hydrocyanic acid is added to the mixture of solvent- and hydrocyanic acid-catalyst in which the reaction has already started (compare German Patent Specification No. 949,060. These known hydrocyanic acid polymers are brown-black to black pulverulent products which are insoluble in all inert solvents, but which dissolve in 1 N aqueous sodium hydroxide solution, with decomposition, even in the cold. A serious disadvantage of hydrocyanic acid polymers of this type is that both when stored under dry conditions and under moist conditions, small amounts of hydrogen cyanide are continuously split off even at room temperature. As the temperature increases, the rate at which hydrogen cyanide is split off also increases. Amounts of hydrocyanic acid which are far above the legally imposed maximum workplace concentration of hydrocyanic acid of 11 ppm therefore even occur in containers holding azulmic acids no matter how mild the storage conditions are. Use in practice of the known hydrocyanic acid polymers for the most diverse purposes thus presents an exceptional danger to the environment and is therefore scarcely possible.
According to a proposal by Th. Volker, the brown-black polymeric hydrocyanic acid (azulmic acid) prepared in water has essentially the following formula (compare Angew. Chem. 72, (1960) pages 379-384): ##STR1##
A degree of polymerization (HCN) of X=15-24 has been calculated from the oxygen contents of known azulmic acids, so that values of 1 to 4 result from m (formula I). The maximum molecular weights achieved for the polymers are slightly above 700.